<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <input name="username" autofocus type="text" placeholder="username" />

    <script>
      let username = document.querySelector("[name=username]");

      username.onblur = function () {
        let reg = new RegExp("^[a-zA-Z]\w{5,9}$");
        // let reg = /^[a-zA-Z]\w{5,9}$/;
        if (reg.test(this.value)) {
          console.log("ok");
        } else {
          console.log("no");
        }
      };
    </script>
  </body>
</html>
